1. Field of the Invention
The present invention relates to a high pressure discharge lamp. More specifically, the present invention relates to a high pressure discharge lamp having a high luminance, a high luminous efficacy, a long life, and high reliability.
2. Description of Related Art
In general, a high pressure discharge lamp has a structure, for instance, as shown in FIG. 2. In the high pressure discharge lamp 1 shown in FIG. 2, each electrode of a pair of electrodes (i.e., an anode 3 and a cathode 4) is disposed so as to be opposite the other in a quartz glass bulb 2, which includes an expanded portion for luminescence 21 and sealing portions 22. The quartz glass bulb 2 is formed by welding the sealing portions 22. The anode 3 and the cathode 4 are joined by, for instance, welding with molybdenum foils 5 and 5xe2x80x2. Also, the sealing portions 22 of the quartz glass bulb 2 are airtightly sealed by, for example, welding with molybdenum foils 5 and 5xe2x80x2. A gas for assisting an electric discharge is contained in the expanded portion for luminescence 21 of the quartz glass bulb 2 which has been airtightly sealed.
High pressure discharge lamps, in general, are required to have characteristics such as a high luminance, a stable and high luminous efficacy, and a long life. As a means for achieving such characteristics of the high pressure discharge lamp from the viewpoint of its shape, the following constitution, for instance, is known as described in the Japanese Unexamined Patent Application, First Publication No. 6-52830.
The high pressure mercury discharge lamp known from the above Japanese patent application includes: a quartz glass lamp vessel having a region surrounding a discharge space; spaced-apart tungsten electrodes disposed in the lamp vessel and defining a discharge path Dp current conductors connected to the electrodes and which extend through the lamp vessel to the exterior; a filling of at least 0.2 mg Hg/mm3, 10xe2x88x926xe2x88x9210xe2x88x924 xcexcmol halogen/mm3 (wherein the halogen is selected from the group consisting of Cl, Br, and I) and a rare gas in the discharge space, the discharge space being spheroidal in shape, having a dimension S in the direction of the discharge path which is S (mm)=e*Di, where e is in the range of 1.0-1.8, Di(mm)=f*(3.2+0.011 (mm/W)*P(W)), where Di is the largest inside diameter of the discharge vessel transverse to the discharge path, f has a value in the range of 0.9-1.1, P is the power consumed at nominal operation, which is in the range of 70-150 W, the lamp vessel having in the region surrounding the discharge space a convex outer surface, which in a plane in which Di is situated has an outside diameter Do which is Doxe2x89xa73.2+0.055 (mm/W)*P(W), the length of the discharge path Dp is in the range of 1.0-2.0 mm, and bromine is the selected halogen.
However, if the above-mentioned constitution for a discharge lamp is used, the thickness of the quartz glass bulb needs to be significantly increased as the level of electric power is increased and this causes an increase in the dispersion of transmitted beams emitted from an outer surface of the quartz glass bulb. Thus, the optical design of the lamp including a reflector becomes difficult and the luminous efficiency of the optical lens is reduced.
Accordingly, one of the objectives of the present invention is to provide a high pressure discharge lamp having an extremely low degree of electrode deterioration, blackening of a quartz glass bulb, and devitrification even if operated under conditions of high luminance, high internal pressure, and high plasma density.
The inventors of the present invention, after pursuing diligent studies to achieve the above-mentioned objectives, have made observation of the ratio of the longest length in the direction of the discharge path of the expanded portion for luminescence to the largest inside diameter of the expanded portion for luminescence transverse to the discharge path, the ratio of the largest inside diameter of the expanded portion for luminescence transverse to the discharge path to the distance between an end of each of the electrodes, and the difference in length between the largest outside diameter of the expanded portion for luminescence transverse to the discharge path and the largest inside diameter thereof. It was discovered that a high pressure discharge lamp having an extremely low degree of electrode deterioration, blackening of the quartz glass bulb, and devitrification even if operated under conditions of high luminance, high internal pressure, and high plasma density may be obtained without adjusting Di or Do according to the level of the electric power if Dp is in the range between about 1.0 and 1.6 mm, S=exc3x97Di (wherein 0.8xe2x89xa6e less than 1.0), Di=gxc3x97Dp (wherein 4xe2x89xa6gxe2x89xa68), and Doxe2x89xa7Di+(4 or more), wherein Dp indicates the distance between an end of each electrode, S indicates the longest length of the expanded portion for luminescence in the direction of the discharge path, Di indicates the largest inside diameter of the expanded portion for luminescence transverse to the discharge path, and Do indicates the largest outside diameter of the expanded portion for luminescence transverse to the discharge path.
It is conventionally known that a high pressure discharge lamp of comparatively stable, comparatively high luminous efficacy, and comparatively long life may be obtained if S is larger than Di, and Di and Do are adjusted to a value corresponding to the level of the electric power. However, the thickness of the quartz glass bulb needs to be significantly increased as the level of power supply is increased, and this causes problems such as a decrease in the luminous efficiency of the lamp. It was absolutely unknown and totally unexpected that such problems may be easily solved, without adjusting Di or Do according to the level of the electric power, by applying a value less than Di to S, and by defining the relationship between Di and Dp and that between Do and Di.
The present invention provides a high pressure discharge lamp including: a quartz glass bulb having an expanded portion and sealing portions; conductive elements, which are airtightly sealed at the sealing portions of the quartz glass bulb; and a pair of electrodes, each electrode of the pair of electrodes being disposed so as to be opposite the other and each electrode being connected to one of the conductive elements; wherein Dp is in the range between about 1.0 and 1.6 mm, S=exc3x97Di (wherein 0.8xe2x89xa6e less than 1.0), Di=gxc3x97Dp (wherein 4xe2x89xa6gxe2x89xa68), and Doxe2x89xa7Di+4,
where Dp indicates the distance between an end of each electrode, S indicates the longest length of the expanded portion in the direction of a discharge path, Di indicates the largest inside diameter of the expanded portion transverse to the discharge path, and Do indicates the largest outside diameter of the expanded portion transverse to the discharge path.
In accordance with another aspect of the invention, the conductive elements are molybdenum foils.
In yet another aspect of the invention, Dp is in the range between about 1.1 and 1.5 mm.
In yet another aspect of the invention, Dp is in the range between about 1.2 and 1.4 mm.
In yet another aspect of the invention, e is in the range of 0.85xe2x89xa6exe2x89xa60.95, and preferably in the range of 0.88xe2x89xa6exe2x89xa60.92.
In yet another aspect of the invention, g is in the range of 4.5xe2x89xa6gxe2x89xa67, and preferably in the range of 5xe2x89xa6gxe2x89xa66.
In yet another aspect of the invention, Doxe2x89xa7Di+5, and preferably Doxe2x89xa7Di+6.
In yet another aspect of the invention, Dp is in the range between 1.1 and 1.5 mm; e is in the range of 0.85xe2x89xa6exe2x89xa60.95; g is in the range of 4.5xe2x89xa6gxe2x89xa67; and Doxe2x89xa7Di+5.
In yet another aspect of the invention, Dp is in the range between 1.2 and 1.4 mm; e is in the range of 0.88xe2x89xa6exe2x89xa60.92; g is in the range of 5xe2x89xa6gxe2x89xa66; and Doxe2x89xa7Di+6.
In yet another aspect of the invention, mercury vapor is contained in the high pressure discharge lamp in an amount between about 0.12 and 0.3 mg/mm3.
In yet another aspect of the invention, a halogen gas is contained in the high pressure discharge lamp in an amount between about 10xe2x88x928 and 10xe2x88x922 xcexcmol/mm3.
In yet another aspect of the invention, an inert gas is contained in the high pressure discharge lamp at a pressure of about 6 kPa or greater.
In yet another aspect of the invention, the bulb wall loading in the high pressure discharge lamp is about 0.8 W/mm2 or greater.
In yet another aspect of the invention, the pair of electrodes comprise tungsten containing potassium oxide.
According to the present invention, it becomes possible to provide a high pressure discharge lamp having an extremely low degree of electrode deterioration, blackening of the quartz glass bulb, and devitrification even if operated under conditions of high luminance, high internal pressure, and high plasma density. Such characteristics of the high pressure discharge lamp become more obvious by restricting Dp, e, g, and Do to a certain range and by selecting mercury vapor to be contained in the high pressure discharge lamp, the halogen gas, the inert gas, the bulb wall loading, and the materials used for the electrodes.